Sea-surface temperatures in the central and eastern tropical Pacific are forecast to increase to record levels during October to December 2026, the World Meteorological Organization says.
The WMO's monthly Global Seasonal Climate Update says El Niño will continue to intensify ahead of its forecast peak in December. It is likely to bring above-average temperatures to much of the globe and to shift rainfall patterns.
The anomaly across the central-eastern equatorial Pacific, the region at the heart of El Niño, is measured by the widely used Niño 3.4 index. It increased markedly from an average of +1.6°C above normal in June 2026 to +2.5°C above normal in August.
For October to December, the seasonal average Niño 3.4 anomaly is forecast to reach approximately +3.7°C, peaking around December. That is the highest since observations began and is stronger than the previous record of +2.6°C in November 2015 to January 2016.
“El Niño is firmly established and strengthening rapidly. WMO forecasts indicate a near-100 per cent likelihood that it will persist through February 2027, potentially being one of the strongest since at least 1950,” said the WMO Secretary-General, Celeste Saulo.
That near-certainty figure is not the output of a single model. It is a consensus across thirteen national and international centres, from Washington to Tokyo to London to Pune, built on real-time exchange of ocean buoy, satellite and radiosonde data coordinated by the WMO.
Saulo also set out what the event is and is not. “El Niño doesn't add new heat to the planet. It releases heat the ocean has already been storing beneath the surface - which is why a strong event so often becomes one of the hottest years measured (as with 2024),” she told the Global Heat Forum in Bangkok. “The ocean it's drawing from is the warmest we've ever measured it. There is simply more heat available to release,” she said.
Other ocean basins are contributing to the seasonal outlook. A positive Indian Ocean Dipole is expected to peak in October and then decline, with an October to December anomaly forecast at about +0.5°C, while sea-surface temperatures in the equatorial Atlantic are forecast to remain above normal.
Earth had the hottest August on record, according to monthly reports from the European Union's Copernicus Climate Service, the US National Oceanic and Atmospheric Administration and NASA. Global sea-surface temperature reached an all-time observed high in August.
The Secretary-General's clarification is worth reading twice, because it establishes that the largest climate event of the year is not a production but a transfer.
No new heat is being made. Heat already held beneath the surface of the Pacific is being moved to where the thermometers are. On a planetary balance sheet the total is unchanged, and the record now forecast for December is a record in the location of the heat rather than in its quantity.
This newspaper regards the ocean's conduct as exemplary. It saved quietly for years in the one account nobody was reading, and is now making a single large withdrawal on a published schedule, peaking in December, with a near-100 per cent likelihood of the account remaining open until February.
Thirteen centres from Washington to Pune have examined the statement and found it in order. Confidence is described as high because the forecasts agree with one another, which is the definition of agreement and a separate question from being right.
The Department of Unnecessary Research notes the index's own trajectory: +1.6°C in June, +2.5°C in August and +3.7°C forecast for the final quarter. The increments are growing, which means the forecast is currently warming faster than the ocean it describes.
The previous record stood at +2.6°C and was set across the turn of 2015 into 2016. It is expected to be beaten by a further 1.1°C by an event that, as the WMO is careful to state, brings nothing new to the planet at all.